A "nanocomposite coating" is a coating having more than one solid phase, in which at least one phase is in the nanometer range. Attention has been directed to nanoparticles and nanocomposites because of the unique properties exhibited by these materials. For example, Silicon (Si) is an indirect band gap semiconductor that can be potentially used for optoelectronic applications such as light emitting devices. Unfortunately, the development of such devices has been hindered since crystalline Si is not an efficient light emitter. However, this changed with the development of porous-Si (por-Si), an irregular network of nanocrystalline Si which exhibits a band gap energy twice the band gap energy of crystalline Si (L. T. Canham, Appl. Phys. Lett. 57(10):1046-1048 (1990)). Thus, the potential applications of semiconductor materials, such as Si, have increased because of the development of nanomaterials.
Typically, nanocrystalline or nanocomposite coatings are produced using chemical techniques such as Chemical Vapor Deposition (CVD), which require gaseous reactants and vacuum chambers to contain the gaseous reactants. However, the use of these gaseous reactants involves safety risks, in addition to time and cost considerations associated with containment of the gaseous reactants. Thus, for mass scale production of nanocrystalline or nanocomposite coatings CVD techniques are not without disadvantages.
An common alternative to CVD is thermal or plasma spraying, which uses a particulate precursor material rather than a reactive gas. Thermal or plasma spray provides a flexible, cost-effective and safer method for producing coatings since gaseous reactants are avoided. Moreover, vacuum chambers are generally avoided since the coatings are typically sprayed at atmospheric pressure.
However, nanocrystalline or nanocomposite coatings produced solely with plasma or thermal spraying have yet to be developed. While combinations of CVD and thermal spraying have been used to produce nanocrystalline coatings (Heberlein et al., Thermal Spray: A United Forum for Scientific and Technological Advances, 329-333 (1997)), reactive precursor gases are still required to form the nanocrystalline coating.
In view of the current state of the art, there is a need for a method of producing nanocrystalline or nanocomposite coatings without reliance on gaseous precursor reactants.
Accordingly, it is an object of the present invention to provide a method of producing nanocomposite coatings without the use of reactive precursor gases. It is also an object of the present invention to provide a method of producing nanocomposite coatings having metastable, high pressure phases of nanocrystalline material.